根据Ia型超新星的线性偏振测量推断河外尘埃的性质
Properties of extragalactic dust inferred from linear polarimetry of Type Ia Supernovae
摘要：
目的：本文的目的是双重的：1）调查河外尘埃的性质，并将其与银河系中所看到的进行比较; 2）以独立的方式解决与爆炸环境有关的Ia型超新星（SN）的异常消光曲线问题。研究方法：尘埃的性质来自于在四个变红的Ia型SN：1986 G，2006 X，2008 fp和2014 J中观察到的连续偏振的波长依赖性。[...]结果如下：这四个天体的特征都是总吸收与选择性吸收的比值（R_V）非常低，并显示出异常的星际偏振规律，其特征是非常蓝的偏振峰。在所有情况下，偏振位置角与局部螺旋结构良好对准。虽然SN~ 1986 G与银河系中已知的最极端的星际极化情况兼容，但SN 2006 X，2008 fp和2014 J表现出前所未有的行为。所观察到的偏差似乎并不连接到选择效果相关的相对大量的红化表征的对象中的样本。结论：造成这四个SN偏振的尘埃很可能是星际性质的。极化特性可以解释为小颗粒的丰度显著增加。这种异常行为显然与SN爆炸的银河系环境的性质有关，而不是与它们起源的祖先系统有关。对于SN 2014 J的极端情况，我们不能排除当地物质散射光的贡献;然而，观察到的偏振特性需要一个特设的几何尘埃分布。
英文摘要：
Aims: The aim of this paper is twofold: 1) to investigate the properties of extragalactic dust and compare them to what is seen in the Galaxy; 2) to address in an independent way the problem of the anomalous extinction curves reported for reddened Type Ia Supernovae (SN) in connection to the environments in which they explode. Methods: The properties of the dust are derived from the wavelength dependence of the continuum polarization observed in four reddened Type Ia SN: 1986G, 2006X, 2008fp, and 2014J. [...] Results: All four objects are characterized by exceptionally low total-to-selective absorption ratios (R_V) and display an anomalous interstellar polarization law, characterized by very blue polarization peaks. In all cases the polarization position angle is well aligned with the local spiral structure. While SN~1986G is compatible with the most extreme cases of interstellar polarization known in the Galaxy, SN2006X, 2008fp, and 2014J show unprecedented behaviours. The observed deviations do not appear to be connected to selection effects related to the relatively large amounts of reddening characterizing the objects in the sample. Conclusions: The dust responsible for the polarization of these four SN is most likely of interstellar nature. The polarization properties can be interpreted in terms of a significantly enhanced abundance of small grains. The anomalous behaviour is apparently associated with the properties of the galactic environment in which the SN explode, rather than with the progenitor system from which they originate. For the extreme case of SN2014J, we cannot exclude the contribution of light scattered by local material; however, the observed polarization properties require an ad hoc geometrical dust distribution.
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